1. Field of the Invention
The present invention relates to a nozzle shut-off valve adapted for use on the injection system of an injection molding machine. More particularly, the present invention relates to a positive action shut-off valve that includes a cylindrical body portion and a sleeve that is slidably carried by the body portion to provide selective communication between a valve inlet and a valve outlet.
2. Description of the Related Art
Nozzle shut-off valves are provided in the forward or discharge end of the plastication barrel of an injection molding machine to control the flow of plasticated material from the barrel. The valves operate to prevent flow of plasticated material from the plastication barrel until a predetermined quantity of plasticated material has been accumulated ahead of the plastication screw to fill a mold cavity. At that point the shut-off valve is opened and the plastication screw or ram is moved axially within the barrel in the direction toward the shut-off valve to inject the plasticated material through the valve and into a mold cavity defined by a mold that is positioned adjacent an outlet nozzle at the discharge end of the plastication barrel.
Various types of shut-off valve structures have been used in the past. For example, U.S. Pat. No. 3,500,501, which issued Mar. 17, 1970, to O. R. Johansson, discloses a pneumatically operated shut-off valve in the form of a spool that is transversely movable relative to a flow passageway, the spool having a transverse throughbore that is selectively alignable with the flow passageway to permit or to prevent flow through the flow passageway, depending upon the position of the throughbore relative to the flow passageway.
In U.S. Pat. No. 3,431,600, which issued Mar. 11, 1969, to C. P. Bullard et al., there is disclosed a nozzle shut-off valve that provides a rotatable ball element having a diametral through passageway, the through passageway being selectively alignable and non-alignable relative to a flow passageway, and an actuating cylinder for rotating the ball member about a horizontal axis to cause the ball passageway to come into and out of alignment with the flow passageway.
U.S. Pat. No. 3,809,519, which issued May 7, 1974, to Paul J. Garner, discloses a nozzle shut-off valve wherein a pair of inlets are selectively connectible with a single outlet. A cylindrical body includes a pair of transversely extending throughbores that are inclined relative to each other, the respective throughbores being alignable with one or the other of the inlets to provide communication between that inlet and the valve outlet.
Although the prior art nozzle shut-off valves have generally functioned in a satisfactory manner, oftentimes they do not serve to provide a positive shut-off of the flow from the plastication barrel. It is therefore an object of the present invention to provide an improved nozzle shut-off valve that provides positive shut-off of flow of plasticated material. It is a further object of the present invention to provide a nozzle shut-off valve that is of simple construction, that has few moving parts, and that is easily controllable.